How to change system font?

I installed Yosemite DP3 because I feel that it's good enough for my daily usage in terms of development (using Xcode and other tools).

However, I do not like the visual changes. I can deal with the new dock, but the system font is hideous. I can barely stand it on stock iOS (that's why I install Bytafont right away after a JB), and seeing it on the desktop is not good. Lucida Grande was fine.

In previous versions of OS X there used to be a way to replace certain files and basically use any font you like (the now deceased MacThemes used to have a huge thread for this). I'm just wondering if it would work to get 10.9's system font files and replace Helvetica Neue once and for all. If not, I'll just downgrade to Mavericks. Thanks!

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